Magnesium chloride supported Ziegler-Matta catalysts are well known in the art. Typically, the magnesium chloride support is prepared by reacting an excess of chloride anion with a dialkylmagnesium compound, so as to provide a magnesium chloride support material which has relatively little or substantially no alkylmagnesium bonds present prior to addition of an active metal species, such as a titanium compound. The use of such catalysts in the polymerization of olefins is discussed, for example, in U.S. Pat. Nos. 4,612,300 and 5,106,805.
For some catalyst preparations a magnesium chloride support is made with a small deficiency in chloride ion. For example U.S. Pat. No. 4,490,475 teaches that in order to generate magnesium chloride support material with pendant Mg—R functionality, the molar ratio in a reaction between an alkyl halide and a dialkylmagnesium should be from 1.85 to 1.95. U.S. Pat. No. 4,497,904 teaches that addition of a reduced titanium species to a magnesium chloride support which has small amounts of alkylmagnesium bonds provides an active ethylene polymerization catalyst. In each of these patents, formation of a “chloride deficient” magnesium chloride support is carried out in the presence of an electron donor such as an oxygen, sulfur, nitrogen or phosphorus compound.
U.S. Pat. No. 4,250,288 discusses the formation of an olefin polymerization catalyst by combining a dialkylmagnesium compound, a source of chloride ion and a tetravalent titanium compound. A broad atomic ratio of magnesium to chloride is claimed for the final catalyst formulation (i.e. from 0.1:1 to 1:1) and with regard to intermediate support formation, the patent teaches that chloride ion is preferably added in amounts which convert all dialkylmagnesium compounds into hydrocarbon insoluble magnesium species.
When making magnesium chloride supports by treating dialkylmagnesium compounds with less than 2 molar equivalents of chloride ion, the presence of un-reacted dialkylmagnesium compound is expected.
In U.S. Pat. No. 7,666,810 it was shown that the presence of dialkylmagnesium species, in mixtures used to prepare magnesium chloride supported Ziegler-Natta catalysts, has a negative impact on catalyst performance. In order to prepare highly active catalysts for high temperature olefin polymerization, a filtration/washing step was used to remove un-reacted dialkylmagnesium species. Although filtration and washing steps are effective, they are time consuming and add cost to the catalyst preparation procedure. Perhaps even more importantly, filtration and washing steps are not a viable option for in-line catalyst preparative methods.
In light of the above, an alternative method which provides a magnesium chloride support which is deficient in chloride and which reduces the amount of un-reacted dialkylmagnesium available to negatively impact catalyst performance would be very useful. It would be especially useful if such a method was compatible with in-line catalyst preparation and delivery procedures. In line methods to prepare a Ziegler-Natta catalyst are taught in, for example, U.S. Pat. No. 6,723,677.
Also useful would be a support and catalyst composition which does not require electron donor compounds to be effective, since electron donor compounds add procedural steps and increase catalyst cost.